There are two types of warning sirens. The first, indicating general disaster, is a continuous oscillating siren lasting around a minute. The second, used to warn people who live downstream of dams of impending water-related catastrophe, is a series of 12 bursts of 20 seconds each at ten-second intervals.

The first warning sirens will be tested at 1.30pm, with tests continuing as necessary until 2pm. The water-emergency related alarms will be tested from 2.15pm until 4pm.

During the testing on February 7th this year a technical problem was discovered in the software used by the centralised system that regulates the alarms, meaning the testing was only a “partial success”, the Federal Office for the Protection of the Population (FPOP) said at the time.

The office said the sirens would still have functioned in the event of a real emergency.